We are currently studying the electrical behavior of a K ion -selective conductance channel from the sarcoplasmic reticulum membrane. The channel may be inserted in an oriented fashion into an artificial phospholipid membrane, and the K ion conductance conferred upon this membrane may be studied. We have found that the channel operated by two-state conformational mechanism; the equilibrium between the two states in sensitive to applied voltage. We have discovered three different ways of inhibiting the channel's conductance: reversible blocking by Ca ions and other divalent cations, reversible, voltage-dependent blocking by Cs ion a " K ion analogue", and irreversible destruction of the conducting structure by Ag ion, mercurials, and transition metal ions. We have also found that certain endopeptidases specific for lysine and arginine residues modify the channel's voltage-dependent properties. We intent to continue this modification work and to begin studies on purifying the channel protein complex. In addition, we are engaged in studies of the electrical properties of individual channels, which may be detected by fluctuation methods.